Processes for the preparation of high-cis polydienes

ABSTRACT

Disclosed herein are solution polymerization processes for producing a high-cis polydiene. The processes include polymerizing at least one conjugated diene monomer in an organic solvent in the presence of at least one thiol compound and a lanthanide-based catalyst composition to produce a polydiene having a cis-1,4-linkage content of 90-99%. The at least one thiol compound is represented by the general formula R—S—H, where R is a hydrocarbyl group or a substituted hydrocarbyl group. The lanthanide-based catalyst composition comprises (a) a lanthanide compound, (b) an alkylating agent, and (c) a halogen source, where (c) may optionally be provided by (a), (b), or both (a) and (b). The molar ratio of the at least one thiol compound to the lanthanide compound used in the polymerization process ranges from 0.01:1 to 100:1. Improved solution polymerization processes regarding the same are also disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/380,944, filed Aug. 26, 2014 and issued as U.S. Pat. No. 9,353,205,which is a national stage application of PCT Application No.PCT/US2013/027905, filed Feb. 27, 2013, which claims priority to and anyother benefit of U.S. Provisional Patent Application Ser. No.61/603,658, filed Feb. 27, 2012, and entitled “PROCESSES FOR THEPREPARATION OF HIGH-CIS POLYDIENES,” the entire disclosures of which areincorporated by reference herein.

FIELD OF THE INVENTION

The disclosure relates to polymerization processes for producingpolydienes having a high cis-1,4-linkage content using alanthanide-based catalyst system.

BACKGROUND

Synthetic polymers that are used in rubber compositions and that undergostrain-induced crystallization provide advantageous propertiesincluding, for example, tensile strength and abrasion resistance in therubber composition. Polydienes with a high cis-1,4-linkage content,which exhibit the increased ability to undergo strain-inducedcrystallization, have been advantageously employed in tires,particularly in the tire components that benefit from such propertiessuch as the sidewall and tread components of tires.

Lanthanide-based catalyst systems comprising a lanthanide compound, analkylating agent, and a halogen source are useful for polymerizingconjugated diene monomers to produce polydienes having a highcis-1,4-linkage content. The polydienes with the high cis-1,4-linkagecontent produced with such catalyst systems have a linear backbonestructure, exhibit good green strength, and have excellent viscoelasticproperties. The linear backbone structure, in turn, is believed toprovide excellent properties directed to improved tensile strength,increased abrasion resistance, lower hysteresis, and improved fatigueresistance in the rubber compositions formed with these polydienes.Thus, the polydienes having the high cis-1,4-linkage content producedusing lanthanide-based catalyst systems are desirable for use in tiresand tire components such as sidewalls and treads.

The polymerization processes disclosed herein provide certain advantagesand improvements to the use of lanthanide-based catalyst systems toproduce polydienes having a high cis-1,4-linkage content. As discussedherein, the present disclosure relates to using a thiol compound incombination with a lanthanide-based catalyst system to producepolydienes having a higher cis-1,4-linkage content as compared topolydienes prepared under the same polymerization conditions but withoutthe thiol compound.

SUMMARY OF THE INVENTION

The present disclosure provides solution polymerization processes forproducing a high-cis polydiene comprising polymerizing at least oneconjugated diene monomer in an organic solvent in the presence of atleast one thiol compound and a lanthanide-based catalyst composition toproduce a polydiene having a cis-1,4-linkage content of 90-99%. The atleast one thiol compound is represented by the general formula R—S—H,where R is a hydrocarbyl group or a substituted hydrocarbyl group. Thelanthanide-based catalyst composition comprises (a) a lanthanidecompound, (b) an alkylating agent, and (c) a halogen source, where (c)may optionally be provided by (a), (b), or both (a) and (b). The molarratio of the at least one thiol compound to the lanthanide compound usedin the polymerization processes ranges from 0.01:1 to 100:1.

Other embodiments of the present disclosure provide improved solutionpolymerization processes for producing a high-cis polydiene by thepolymerization of at least one conjugated diene monomer in an organicsolvent charged with a lanthanide-based catalyst composition. Theimproved processes comprise polymerizing the at least one conjugateddiene monomer in the presence of at least one thiol compound in theorganic solvent charged with the lanthanide-based catalyst compositionto produce a polydiene having a cis-1,4-linkage content of 90-99%. Theimprovement is shown in the resulting polydiene, where the polydieneproduced has a higher cis-1,4-linkage content compared to a polydieneproduced under the same polymerization conditions but without the atleast one thiol compound. In accordance with embodiments disclosedherein, the at least one thiol compound is represented by the generalformula R—S—H, where R is a hydrocarbyl group or a substitutedhydrocarbyl group. Also, the molar ratio of the at least one thiolcompound to the lanthanide compound used in the improved polymerizationprocesses ranges from 0.01:1 to 100:1.

Other aspects of the present disclosure will be apparent from thedescription that follows.

DETAILED DESCRIPTION

The present disclosure is directed to solution polymerization processesfor producing high-cis polydienes from conjugated diene monomers using alanthanide-based catalyst system in combination with a thiol compound.The lanthanide-based catalyst system comprises (a) a lanthanidecompound, (b) an alkylating agent, and (c) a halogen source. A polydieneproduced in accordance with the processes disclosed herein has a highercis-1,4-linkage content as compared to a polydiene produced under thesame polymerization conditions but without the thiol compound. The thiolcompound acts as a catalyst modifier to increase the relativecis-1,4-linkage content of the polydiene. Thus, the use of the thiolcompound with the lanthanide-based catalyst system is an improvement inthe use of lanthanide-based catalyst systems to produce high-cispolydienes.

Polydienes generally contain cis-1,4-, trans-1,4-, and 1,2-linkagesbetween monomer units. As used herein, the term “high-cis” refers to acis-1,4-linkage content of 90-99% in the polydiene. In accordance withcertain embodiments of the process disclosed herein, the resultinghigh-cis polydiene has a cis-1,4-linkage content of 94-99%, preferably96-99%, and more preferably 97-99%. In accordance with one embodiment,the cis-1,4-linkage content ranges from 94% to 99%. In otherembodiments, the cis-1,4-linkage content may range from 97-99%. Thecis-1,4-linkage contents disclosed herein are determined by FTIR(Fourier transform infrared spectroscopy). In particular, the polymersamples are dissolved in CS₂ and then subjected to FTIR.

The polymerization processes described herein are solutionpolymerization processes. In this type of polymerization process, thepolymerization reaction takes place in organic solvent-based solution.Here, that organic solvent-based solution contains at least oneconjugated diene monomer, a lanthanide-based catalyst composition, andat least one thiol compound. The organic solvent-based solutioncomprises 20-90% by weight (wt %) organic solvent based on the totalweight of the monomer, organic solvent, and polydiene in the solution.Preferably, the organic solvent comprises the predominant component ofthe solution, i.e., 50-90 wt % organic solvent, and more preferably 70wt % to 90 wt % organic solvent based on the total weight of themonomer, organic solvent, and polydiene. The solution polymerizationprocesses disclosed herein can be contrasted with gas-type or bulk-typepolymerizations, where polymerization is carried out in the absence ofany organic solvent or where there is less than 20 wt % organic solventpresent based on the total weight of the monomer, organic solvent, andpolydiene.

Suitable organic solvents for use in the solution polymerizationprocesses described herein are those solvents that are inert to thepolymerization reaction such that the solvent is not a reactant in thepolymerization reaction. Suitable organic solvents include aromatichydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons.Examples of suitable aromatic hydrocarbon solvents include, but are notlimited to benzene, toluene, ethylbenzene, diethylbenzene, naphthalenes,mesitylene, xylenes, and the like. Examples of suitable aliphatichydrocarbon solvents include, but are not limited to, n-pentane,n-hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, hexanes,isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, petroleumether, kerosene, petroleum spirits, and the like. Non-limiting examplesof suitable cycloaliphatic hydrocarbon solvents include cyclopentane,cyclohexane, methylcyclopentane, methylcyclohexane, and the like.Mixtures of the foregoing aromatic hydrocarbon solvents, aliphatichydrocarbon solvents, and cycloaliphatic hydrocarbon solvents can alsobe used. In certain embodiments, the preferred organic solvent includesan aliphatic hydrocarbon solvent, a cycloaliphatic hydrocarbon solvent,or mixtures thereof. Additional useful organic solvents suitable for usein the processes disclosed herein are known to those skilled in the art.

The monomer used in accordance with the polymerization processesdescribed herein is a conjugated diene monomer. A conjugated dienemonomer is a hydrocarbon compound that contains at least two doublebonds that are separated by a single bond. Suitable conjugated dienemonomers used with the solution polymerization processes generallyinclude hydrocarbon compounds containing less than 20 carbon atoms.Non-limiting examples of such suitable conjugated diene monomers include1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, 2,4-hexadiene, and combinations thereof. Inaccordance with one embodiment, the polymerization processes disclosedherein utilize at least one conjugated diene to form a high-cispolydiene. In certain embodiments, the polymerization processesdisclosed herein can be utilized for the copolymerization of two or moreconjugated dienes to form copolymers having a cis-1,4-microstructure. Inaccordance with other embodiments, the conjugated diene monomer is1,3-butadiene, resulting in a high-cis polybutadiene afterpolymerization. Additional useful conjugated diene monomers suitable foruse in the processes disclosed herein are known to those skilled in theart.

The thiol compound is used as a catalyst modifier to increase thecis-1,4-linkage content of polydienes produced using a lanthanide-basedcatalyst composition system. In accordance with the polymerizationprocesses disclosed herein, the lanthanide-based catalyst compositioncomprises (a) a lanthanide compound, i.e. a lanthanide-containingcompound, (b) an alkylating agent, and (c) a halogen source. In suchcatalyst system, the halogen source may optionally be provided by thelanthanide compound, the alkylating agent, or both the lanthanidecompound and the alkylating agent. In other words, in certainembodiments, there may be no separate (c) component.

As mentioned above, the lanthanide-based catalyst composition systememployed in the polymerization processes includes a lanthanide compound.Lanthanide compounds useful in the polymerization processes disclosedherein are those compounds that include at least one atom of alanthanide element. As used herein, “lanthanide element” refers theelements found in the lanthanide series of the Periodic Table (i.e.,element numbers 57-71) as well as didymium, which is a mixture ofrare-earth elements obtained from monazite sand. In particular, thelanthanide elements as disclosed herein include lanthanum, neodymium,cerium, praseodymium, promethium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, anddidymium. Preferably, the lanthanide compound includes at least one atomof neodymium, gadolinium, samarium, or combinations thereof.

The lanthanide atom in the lanthanide compound can be in variousoxidation states including, but not limited to, the 0, +2, +3, and +4oxidation states. In accordance with certain embodiments of thepolymerization processes disclosed herein, a trivalent lanthanidecompound, where the lanthanide atom is in the +3 oxidation state, isused. Generally, suitable lanthanide compounds for use in thepolymerization processes disclosed herein include, but are not limitedto, lanthanide carboxylates, lanthanide organophosphates, lanthanideorganophosphonates, lanthanide organophosphinates, lanthanidecarbamates, lanthanide dithiocarbamates, lanthanide xanthates,lanthanide β-diketonates, lanthanide alkoxides or aryloxides, lanthanidehalides, lanthanide pseudo-halides, lanthanide oxyhalides, andorganolanthanide compounds.

In accordance with certain embodiments of the polymerization processesdisclosed herein, the lanthanide compounds may be soluble in hydrocarbonsolvents such as the aromatic hydrocarbon solvents, aliphatichydrocarbon solvents, or cycloaliphatic hydrocarbon solvents disclosedherein. Hydrocarbon-insoluble lanthanide compounds, however, can also beuseful in the present polymerization process, as they can be suspendedin the polymerization medium to form the catalytically active species.

For ease of illustration, further discussion of useful lanthanidecompounds for use in the polymerization processes disclosed herein willfocus on neodymium compounds, although those skilled in the art will beable to select similar compounds that are based upon the otherlanthanide metals disclosed herein.

Examples of suitable neodymium carboxylates for use as the lanthanidecompound in the polymerization processes disclosed herein include, butare not limited to, neodymium formate, neodymium acetate, neodymiumacrylate, neodymium methacrylate, neodymium valerate, neodymiumgluconate, neodymium citrate, neodymium fumarate, neodymium lactate,neodymium maleate, neodymium oxalate, neodymium 2-ethylhexanoate,neodymium neodecanoate (i.e., neodymium versatate or NdV₃), neodymiumnaphthenate, neodymium stearate, neodymium oleate, neodymium benzoate,and neodymium picolinate.

Examples of suitable neodymium organophosphates for use as thelanthanide compound in the polymerization processes disclosed hereininclude, but are not limited to, neodymium dibutyl phosphate, neodymiumdipentyl phosphate, neodymium dihexyl phosphate, neodymium diheptylphosphate, neodymium dioctyl phosphate, neodymiumbis(1-methylheptyl)phosphate, neodymium bis(2-ethylhexyl)phosphate,neodymium didecyl phosphate, neodymium didodecyl phosphate, neodymiumdioctadecyl phosphate, neodymium dioleyl phosphate, neodymium diphenylphosphate, neodymium bis(p-nonylphenyl)phosphate, neodymium butyl(2-ethylhexyl)phosphate, neodymium (1-methylheptyl)(2-ethylhexyl)phosphate, and neodymium (2-ethylhexyl)(p-nonylphenyl)phosphate.

Examples of suitable neodymium organophosphonates for use as thelanthanide compound in the polymerization processes disclosed hereininclude, but are not limited to, neodymium butyl phosphonate, neodymiumpentyl phosphonate, neodymium hexyl phosphonate, neodymium heptylphosphonate, neodymium octyl phosphonate, neodymium(1-methylheptyl)phosphonate, neodymium (2-ethylhexyl)phosphonate,neodymium decyl phosphonate, neodymium dodecyl phosphonate, neodymiumoctadecyl phosphonate, neodymium oleyl phosphonate, neodymium phenylphosphonate, neodymium (p-nonylphenyl)phosphonate, neodymium butylbutylphosphonate, neodymium pentyl pentylphosphonate, neodymium hexylhexylphosphonate, neodymium heptyl heptylphosphonate, neodymium octyloctylphosphonate, neodymium (1-methylheptyl)(1-methylheptyl)phosphonate, neodymium (2-ethylhexyl)(2-ethylhexyl)phosphonate, neodymium decyl decylphosphonate, neodymiumdodecyl dodecylphosphonate, neodymium octadecyl octadecylphosphonate,neodymium oleyl oleylphosphonate, neodymium phenyl phenylphosphonate,neodymium (p-nonylphenyl) (p-nonylphenyl)phosphonate, neodymium butyl(2-ethylhexyl)phosphonate, neodymium (2-ethylhexyl)butylphosphonate,neodymium (1-methylheptyl) (2-ethylhexyl)phosphonate, neodymium(2-ethylhexyl) (1-methylheptyl)phosphonate, neodymium (2-ethylhexyl)(p-nonylphenyl)phosphonate, and neodymium (p-nonylphenyl)(2-ethylhexyl)phosphonate.

Examples of suitable neodymium organophosphinates for use as thelanthanide compound in the polymerization processes disclosed hereininclude, but are not limited to, neodymium butylphosphinate, neodymiumpentylphosphinate, neodymium hexylphosphinate, neodymiumheptylphosphinate, neodymium octylphosphinate, neodymium(1-methylheptyl)phosphinate, neodymium (2-ethylhexyl)phosphinate,neodymium decylphosphinate, neodymium dodecylphosphinate, neodymiumoctadecylphosphinate, neodymium oleylphosphinate, neodymiumphenylphosphinate, neodymium (p-nonylphenyl)phosphinate, neodymiumdibutylphosphinate, neodymium dipentylphosphinate, neodymiumdihexylphosphinate, neodymium diheptylphosphinate, neodymiumdioctylphosphinate, neodymium bis(1-methylheptyl)phosphinate, neodymiumbis(2-ethylhexyl)phosphinate, neodymium didecylphosphinate, neodymiumdidodecylphosphinate, neodymium dioctadecylphosphinate, neodymiumdioleylphosphinate, neodymium diphenylphosphinate, neodymiumbis(p-nonylphenyl)phosphinate, neodymium butyl(2-ethylhexyl)phosphinate, neodymium(1-methylheptyl)(2-ethylhexyl)phosphinate, and neodymium(2-ethylhexyl)(p-nonylphenyl)phosphinate.

Examples of suitable neodymium carbamates for use as the lanthanidecompound in the polymerization processes disclosed herein include, butare not limited to, neodymium dimethylcarbamate, neodymiumdiethylcarbamate, neodymium diisopropylcarbamate, neodymiumdibutylcarbamate, and neodymium dibenzylcarbamate.

Examples of suitable neodymium dithiocarbamates for use as thelanthanide compound in the polymerization processes disclosed hereininclude, but are not limited to, neodymium dimethyldithiocarbamate,neodymium diethyldithiocarbamate, neodymium diisopropyldithiocarbamate,neodymium dibutyldithiocarbamate, and neodymium dibenzyldithiocarbamate.

Examples of suitable neodymium xanthates for use as the lanthanidecompound in the polymerization processes disclosed herein include, butare not limited to, neodymium methylxanthate, neodymium ethylxanthate,neodymium isopropylxanthate, neodymium butylxanthate, and neodymiumbenzylxanthate.

Examples of suitable neodymium β-diketonates for use as the lanthanidecompound in the polymerization processes disclosed herein include, butare not limited to, neodymium acetylacetonate, neodymiumtrifluoroacetylacetonate, neodymium hexafluoroacetylacetonate, neodymiumbenzoylacetonate, and neodymium 2,2,6,6-tetramethyl-3,5-heptanedionate.

Examples of suitable neodymium alkoxides or aryloxides for use as thelanthanide compound in the polymerization processes disclosed hereininclude, but are not limited to, neodymium methoxide, neodymiumethoxide, neodymium isopropoxide, neodymium 2-ethylhexoxide, neodymiumphenoxide, neodymium nonylphenoxide, and neodymium naphthoxide.

Examples of suitable neodymium halides for use as the lanthanidecompound in the polymerization processes disclosed herein include, butare not limited to, neodymium fluoride, neodymium chloride, neodymiumbromide, and neodymium iodide. Suitable neodymium pseudo-halidesinclude, but are not limited to, neodymium cyanide, neodymium cyanate,neodymium thiocyanate, neodymium azide, and neodymium ferrocyanide.Suitable neodymium oxyhalides include, but are not limited to, neodymiumoxyfluoride, neodymium oxychloride, and neodymium oxybromide. A Lewisbase, such as tetrahydrofuran (“THF”), can be employed as an aid forsolubilizing this class of neodymium compounds in inert organicsolvents. Where lanthanide halides, lanthanide oxyhalides, or otherlanthanide compounds containing a halogen atom are used, the lanthanidecompound may optionally also provide all or part of the halogen sourcein the lanthanide-based catalyst composition system.

As used herein, the term “organolanthanide compound” refers to anylanthanide compound containing at least one lanthanide-carbon bond.These compounds are predominantly, though not exclusively, thosecontaining cyclopentadienyl (“Cp”), substituted cyclopentadienyl, allyl,and substituted allyl ligands. Suitable organolanthanide compounds foruse as the lanthanide compound in the polymerization processes disclosedherein include, but are not limited to, Cp₃Ln, Cp₂LnR, Cp₂LnCl, CpLnCl₂,CpLn (cyclooctatetraene), (C₅Me₅)₂LnR, LnR₃, Ln(allyl)₃, andLn(allyl)₂Cl, where Ln represents a lanthanide atom, and R represents ahydrocarbyl group or a substituted hydrocarbyl group. In one or moreembodiments, hydrocarbyl groups or substituted hydrocarbyl groups usefulin the polymerization processes disclosed herein may contain heteroatomssuch as, for example, nitrogen, oxygen, boron, silicon, sulfur, andphosphorus atoms.

As mentioned above, the lanthanide-based catalyst composition systememployed in the polymerization processes disclosed herein includes analkylating agent. In accordance with one or more embodiments of thepresent processes, alkylating agents, which may also be referred to ashydrocarbylating agents, include organometallic compounds that cantransfer one or more hydrocarbyl groups to another metal. Generally,these agents include organometallic compounds of electropositive metalssuch as Groups 1, 2, and 3 metals (Groups IA, IIA, and IIIA metals).Alkylating agents useful in the polymerization processes disclosedherein include, but are not limited to, organoaluminum andorganomagnesium compounds. As used herein, the term “organoaluminumcompound” refers to any aluminum-containing compound having at least onealuminum-carbon bond. In one or more embodiments, organoaluminumcompounds that are soluble in a hydrocarbon solvent can be used. As usedherein, the term “organomagnesium compound” refers to anymagnesium-containing compound having at least one magnesium-carbon bond.In one or more embodiments, organomagnesium compounds that are solublein a hydrocarbon can be used. As will be described in more detail below,certain suitable alkylating agents may be in the form of a halidecompound. Where the alkylating agent includes a halogen atom, thealkylating agent may optionally also provide all or part of the halogensource in the lanthanide-based catalyst composition system.

In one or more embodiments of the polymerization processes disclosedherein, organoaluminum compounds that are utilized include thoserepresented by the general formula AlR_(n)X_(3-n), where each Rindependently is a monovalent organic group that is attached to thealuminum atom via a carbon atom; where each X independently is ahydrogen atom, a halogen atom, a carboxylate group, an alkoxide group,or an aryloxide group; and where n is an integer in the range of from 1to 3. In one or more embodiments, each R independently is a hydrocarbylgroup or a substituted hydrocarbyl group including, but not limited to,alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl,allyl, and alkynyl groups, with each group containing from 1 carbonatom, or the appropriate minimum number of atoms to form the group, upto 20 carbon atoms. These hydrocarbyl groups or substituted hydrocarbylgroups may contain heteroatoms including, but not limited to, nitrogen,oxygen, boron, silicon, sulfur, and phosphorus atoms.

Examples of types of organoaluminum compounds for use as the alkylatingagent in the polymerization processes disclosed herein that arerepresented by the general formula AlR_(n)X_(3-n) include, but are notlimited to, trihydrocarbylaluminum, dihydrocarbylaluminum hydride,hydrocarbylaluminum dihydride, dihydrocarbylaluminum carboxylate,hydrocarbylaluminum bis(carboxylate), dihydrocarbylaluminum alkoxide,hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum halide,hydrocarbylaluminum dihalide, dihydrocarbylaluminum aryloxide, andhydrocarbylaluminum diaryloxide compounds.

Examples of suitable trihydrocarbylaluminum compounds for use as thealkylating agent in the polymerization processes disclosed hereininclude, but are not limited to, trimethylaluminum, triethylaluminum,triisobutylaluminum, tri-n-propylaluminum, triisopropylaluminum,tri-n-butylaluminum, tri-t-butylaluminum, tri-n-pentylaluminum,trineopentylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum,tris(2-ethylhexyl)aluminum, tricyclohexylaluminum, tris(1-methylcyclopentyl)aluminum, triphenylaluminum, tri-p-tolylaluminum,tris(2,6-dimethylphenyl)aluminum, tribenzylaluminum,diethylphenylaluminum, diethyl-p-tolylaluminum, diethylbenzylaluminum,ethyldiphenylaluminum, ethyldi-p-tolylaluminum, andethyldibenzylaluminum.

Examples of suitable dihydrocarbylaluminum hydride compounds for use asthe alkylating agent in the polymerization processes disclosed hereininclude, but are not limited to, diethylaluminum hydride,di-n-propylaluminum hydride, diisopropylaluminum hydride,di-n-butylaluminum hydride, diisobutylaluminum hydride,di-n-octylaluminum hydride, diphenylaluminum hydride, di-p-tolylaluminumhydride, dibenzylaluminum hydride, phenylethylaluminum hydride,phenyl-n-propylaluminum hydride, phenylisopropylaluminum hydride,phenyl-n-butylaluminum hydride, phenylisobutylaluminum hydride,phenyl-n-octylaluminum hydride, p-tolylethylaluminum hydride,p-tolyl-n-propylaluminum hydride, p-tolylisopropyl aluminum hydride,p-tolyl-n-butylaluminum hydride, p-tolylisobutylaluminum hydride,p-tolyl-n-octylaluminum hydride, benzylethylaluminum hydride,benzyl-n-propylaluminum hydride, benzylisopropylaluminum hydride,benzyl-n-butylaluminum hydride, benzylisobutylaluminum hydride, andbenzyl-n-octylaluminum hydride.

Examples of suitable hydrocarbylaluminum dihydrides for use as thealkylating agent in the polymerization processes disclosed hereininclude, but are not limited to, ethylaluminum dihydride,n-propylaluminum dihydride, isopropylaluminum dihydride, n-butylaluminumdihydride, isobutylaluminum dihydride, and n-octylaluminum dihydride.

Examples of suitable dihydrocarbylaluminum halide compounds for use asthe alkylating agent in the polymerization processes disclosed hereininclude, but are not limited to, diethylaluminum chloride,di-n-propylaluminum chloride, diisopropylaluminum chloride,di-n-butylaluminum chloride, diisobutylaluminum chloride,di-n-octylaluminum chloride, diphenylaluminum chloride,di-p-tolylaluminum chloride, dibenzylaluminum chloride,phenylethylaluminum chloride, phenyl-n-propylaluminum chloride,phenylisopropylaluminum chloride, phenyl-n-butylaluminum chloride,phenylisobutylaluminum chloride, phenyl-n-octylaluminum chloride,p-tolylethylaluminum chloride, p-tolyl-n-propylaluminum chloride,p-tolylisopropylaluminum chloride, p-tolyl-n-butylaluminum chloride,p-tolylisobutylaluminum chloride, p-tolyl-n-octylaluminum chloride,benzylethylaluminum chloride, benzyl-n-propylaluminum chloride,benzylisopropylaluminum chloride, benzyl-n-butylaluminum chloride,benzylisobutylaluminum chloride, and benzyl-n-octylaluminum chloride.

Examples of suitable hydrocarbylaluminum dihalide compounds for use asthe alkylating agent in the polymerization processes disclosed hereininclude, but are not limited to, ethylaluminum dichloride,n-propylaluminum dichloride, isopropylaluminum dichloride,n-butylaluminum dichloride, isobutylaluminum dichloride, andn-octylaluminum dichloride.

Examples of other suitable organoaluminum compounds for use as thealkylating agent in the polymerization processes disclosed herein thatare represented by the general formula AlR_(n)X_(3-n) include, but arenot limited to, dimethylaluminum hexanoate, diethylaluminum octoate,diisobutylaluminum 2-ethylhexanoate, dimethylaluminum neodecanoate,diethylaluminum stearate, diisobutylaluminum oleate, methylaluminumbis(hexanoate), ethylaluminum bis(octoate), isobutylaluminumbis(2-ethylhexanoate), methylaluminum bis(neodecanoate), ethylaluminumbis(stearate), isobutylaluminum bis(oleate), dimethylaluminum methoxide,diethylaluminum methoxide, diisobutylaluminum methoxide,dimethylaluminum ethoxide, diethylaluminum ethoxide, diisobutylaluminumethoxide, dimethylaluminum phenoxide, diethylaluminum phenoxide,diisobutylaluminum phenoxide, methylaluminum dimethoxide, ethylaluminumdimethoxide, isobutylaluminum dimethoxide, methylaluminum diethoxide,ethylaluminum diethoxide, isobutylaluminum diethoxide, methylaluminumdiphenoxide, ethylaluminum diphenoxide, and isobutylaluminumdiphenoxide.

Another class of organoaluminum compounds suitable for use as analkylating agent in the polymerization processes disclosed herein isaluminoxanes. Suitable aluminoxanes include oligomeric linearaluminoxanes, which can be represented by the general formula:

and oligomeric cyclic aluminoxanes, which can be represented by thegeneral formula:

where x is an integer in the range of from 1 to 100, or 10 to 50; y isan integer in the range of from 2 to 100, or 3 to 20; and where each Rindependently is a monovalent organic group that is attached to thealuminum atom via a carbon atom. In one embodiment of the polymerizationprocesses disclosed herein, each R independently is a hydrocarbyl groupor a substituted hydrocarbyl group including, but not limited to, alkyl,cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substitutedcycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, andalkynyl groups, with each group preferably containing from 1 carbonatom, or the appropriate minimum number of atoms to form the group, upto 20 carbon atoms. These hydrocarbyl groups or substituted hydrocarbylgroups may also contain heteroatoms including, but not limited to,nitrogen, oxygen, boron, silicon, sulfur, and phosphorus atoms. As usedherein, the number of moles of the aluminoxane refers to the number ofmoles of the aluminum atoms rather than the number of moles of theoligomeric aluminoxane molecules. This convention is commonly employedin the art of catalyst systems utilizing aluminoxanes.

Aluminoxanes can be prepared by reacting trihydrocarbylaluminumcompounds with water. This reaction can be performed according to knownmethods, such as, for example, (1) a method in which thetrihydrocarbylaluminum compound is dissolved in an organic solvent andthen contacted with water, (2) a method in which thetrihydrocarbylaluminum compound is reacted with water of crystallizationcontained in, for example, metal salts, or water adsorbed in inorganicor organic compounds, or (3) a method in which thetrihydrocarbylaluminum compound is reacted with water in the presence ofthe monomer or monomer solution that is to be polymerized.

Examples of suitable aluminoxane compounds for use as the alkylatingagent in the polymerization processes disclosed herein include, but arenot limited to, methylaluminoxane (“MAO”), modified methylaluminoxane(“MMAO”), ethylaluminoxane, n-propylaluminoxane, isopropylaluminoxane,butylaluminoxane, isobutylaluminoxane, n-pentylaluminoxane,neopentylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane,2-ethylhexylaluminoxane, cyclohexylaluminoxane,1-methylcyclopentylaluminoxane, phenylaluminoxane, and2,6-dimethylphenylaluminoxane. Modified methylaluminoxane can be formedby substituting from 20 to 80 percent of the methyl groups ofmethylaluminoxane with C₂ to C₁₂ hydrocarbyl groups, preferably withisobutyl groups, by using techniques known to those skilled in the art.

In accordance with certain embodiments of the polymerization processesdisclosed herein, aluminoxanes can be used alone or in combination withother organoaluminum compounds. In one embodiment, methylaluminoxane andat least one organoaluminum compound other than aluminoxane, e.g., anorganoaluminum compound represented by AlR_(n)X_(3-n), are used incombination as the alkylating agent. In accordance with this and otherembodiments, the alkylating agent comprises a dihydrocarbylaluminumhydride, a dihydrocarbylaluminum halide, an aluminoxane, or combinationsthereof. For example, in accordance with one embodiment, the alkylatingagent comprises diisobutylaluminum hydride, diethylaluminum chloride,methylaluminoxane, or combinations thereof. U.S. Pat. No. 8,017,695,which is incorporated herein by reference in its entirety, providesother examples where aluminoxanes and organoaluminum compounds can beemployed in combination.

As mentioned above, suitable alkylating agents used in the presentpolymerization processes include organomagnesium compounds. Inaccordance with one or more embodiments, of the polymerization processesdisclosed herein, suitable organomagnesium compounds include thoserepresented by the general formula MgR₂, where each R independently is amonovalent organic group that is attached to the magnesium atom via acarbon atom. In one or more embodiments, each R independently is ahydrocarbyl group or a substituted hydrocarbyl group including, but notlimited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl,cycloalkenyl, substituted cycloalkenyl, aryl, allyl, substituted aryl,aralkyl, alkaryl, and alkynyl groups, with each group preferablycontaining from 1 carbon atom, or the appropriate minimum number ofatoms to form the group, up to 20 carbon atoms. These hydrocarbyl groupsor substituted hydrocarbyl groups may also contain heteroatomsincluding, but not limited to, nitrogen, oxygen, silicon, sulfur, andphosphorus atoms.

Examples of suitable organomagnesium compounds for use as the alkylatingagent in the polymerization processes disclosed herein that arerepresented by the general formula MgR₂ include, but are not limited to,diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium,dibutylmagnesium, dihexylmagnesium, diphenylmagnesium, anddibenzylmagnesium.

Another class of organomagnesium compounds suitable for use as analkylating agent in accordance with embodiments of the polymerizationprocesses disclosed herein is represented by the general formula RMgX,where R is a monovalent organic group that is attached to the magnesiumatom via a carbon atom, and X is a hydrogen atom, a halogen atom, acarboxylate group, an alkoxide group, or an aryloxide group. In one ormore embodiments, R is a hydrocarbyl group or a substituted hydrocarbylgroup including, but not limited to, alkyl, cycloalkyl, substitutedcycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl,allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups, with eachgroup containing from 1 carbon atom, or the appropriate minimum numberof atoms to form the group, up to 20 carbon atoms. These hydrocarbylgroups or substituted hydrocarbyl groups may also contain heteroatomsincluding, but not limited to, nitrogen, oxygen, boron, silicon, sulfur,and phosphorus atoms. In one embodiment, X is a carboxylate group, analkoxide group, or an aryloxide group, with each group containing from 1carbon atom up to 20 carbon atoms.

Examples of suitable types of organomagnesium compounds for use as thealkylating agent in the polymerization processes disclosed herein thatare represented by the general formula RMgX include, but are not limitedto, hydrocarbylmagnesium hydride, hydrocarbylmagnesium halide,hydrocarbylmagnesium carboxylate, hydrocarbylmagnesium alkoxide, andhydrocarbylmagnesium aryloxide.

Examples of suitable organomagnesium compounds for use as the alkylatingagent in the polymerization processes disclosed herein represented bythe general formula RMgX include, but are not limited to,methylmagnesium hydride, ethylmagnesium hydride, butylmagnesium hydride,hexylmagnesium hydride, phenylmagnesium hydride, benzylmagnesiumhydride, methylmagnesium chloride, ethylmagnesium chloride,butylmagnesium chloride, hexylmagnesium chloride, phenylmagnesiumchloride, benzylmagnesium chloride, methylmagnesium bromide,ethylmagnesium bromide, butylmagnesium bromide, hexylmagnesium bromide,phenylmagnesium bromide, benzylmagnesium bromide, methylmagnesiumhexanoate, ethylmagnesium hexanoate, butylmagnesium hexanoate,hexylmagnesium hexanoate, phenylmagnesium hexanoate, benzylmagnesiumhexanoate, methylmagnesium ethoxide, ethylmagnesium ethoxide,butylmagnesium ethoxide, hexylmagnesium ethoxide, phenylmagnesiumethoxide, benzylmagnesium ethoxide, methylmagnesium phenoxide,ethylmagnesium phenoxide, butylmagnesium phenoxide, hexylmagnesiumphenoxide, phenylmagnesium phenoxide, and benzylmagnesium phenoxide.

As mentioned above, the lanthanide-based catalyst systems employed inthe polymerization processes disclosed herein include a halogen source.As used herein, the term “halogen source” refers to any substanceincluding at least one halogen atom. In accordance with one or moreembodiments of the polymerization processes disclosed herein, all orpart of the halogen source may optionally be provided by the lanthanidecompound, the alkylating agent, or both the lanthanide compound and thealkylating agent. In other words, the lanthanide compound may serve asboth the lanthanide compound and all or at least a portion of thehalogen source. Similarly, the alkylating agent may serve as both thealkylating agent and all or at least a portion of the halogen source.

In accordance with certain embodiments of the polymerization processesdisclosed herein, at least a portion of the halogen source may bepresent in the catalyst system in the form of a separate and distincthalogen-containing compound. Various compounds, or mixtures thereof,that contain one or more halogen atoms can be used as the halogensource. Examples of halogen atoms include, but are not limited to,fluorine, chlorine, bromine, and iodine. A combination of two or morehalogen atoms can also be utilized. Halogen-containing compounds thatare soluble in an organic solvent, such as the aromatic hydrocarbon,aliphatic hydrocarbon, and cycloaliphatic hydrocarbon solvents disclosedherein, are suitable for use as the halogen source in the polymerizationprocesses disclosed herein. In addition, hydrocarbon-insolublehalogen-containing compounds that can be suspended in a polymerizationsystem to form the catalytically active species are also useful incertain embodiment of the polymerization processes disclosed herein.

Examples of suitable types of halogen-containing compounds for use inthe polymerization processes disclosed herein include, but are notlimited to, elemental halogens, mixed halogens, hydrogen halides,organic halides, inorganic halides, metallic halides, and organometallichalides.

Examples of elemental halogens suitable for use as the halogen source inthe polymerization processes disclosed herein include, but are notlimited to, fluorine, chlorine, bromine, and iodine. Some specificexamples of suitable mixed halogens include, but are not limited to,iodine monochloride, iodine monobromide, iodine trichloride, and iodinepentafluoride.

Examples of suitable hydrogen halides for use as the halogen source inthe polymerization processes disclosed herein include, but are notlimited to, hydrogen fluoride, hydrogen chloride, hydrogen bromide, andhydrogen iodide.

Examples of suitable organic halides for use as the halogen source inthe polymerization processes disclosed herein include, but are notlimited to, t-butyl chloride, t-butyl bromide, allyl chloride, allylbromide, benzyl chloride, benzyl bromide, chloro-di-phenylmethane,bromo-di-phenylmethane, triphenylmethyl chloride, triphenylmethylbromide, benzylidene chloride, benzylidene bromide,methyltrichlorosilane, phenyltrichlorosilane, dimethyldichlorosilane,diphenyldichlorosilane, trimethylchlorosilane, benzoyl chloride, benzoylbromide, propionyl chloride, propionyl bromide, methyl chloroformate,and methyl bromoformate.

Examples of suitable inorganic halides for use as the halogen source inthe polymerization processes disclosed herein include, but are notlimited to, phosphorus trichloride, phosphorus tribromide, phosphoruspentachloride, phosphorus oxychloride, phosphorus oxybromide, borontrifluoride, boron trichloride, boron tribromide, silicon tetrafluoride,silicon tetrachloride, silicon tetrabromide, silicon tetraiodide,arsenic trichloride, arsenic tribromide, arsenic triiodide, seleniumtetrachloride, selenium tetrabromide, tellurium tetrachloride, telluriumtetrabromide, and tellurium tetraiodide.

Examples of suitable metallic halides for use as the halogen source inthe polymerization processes disclosed herein include, but are notlimited to, tin tetrachloride, tin tetrabromide, aluminum trichloride,aluminum tribromide, antimony trichloride, antimony pentachloride,antimony tribromide, aluminum triiodide, aluminum trifluoride, galliumtrichloride, gallium tribromide, gallium triiodide, gallium trifluoride,indium trichloride, indium tribromide, indium triiodide, indiumtrifluoride, titanium tetrachloride, titanium tetrabromide, titaniumtetraiodide, zinc dichloride, zinc dibromide, zinc diiodide, and zincdifluoride.

Examples of suitable organometallic halides for use as the halogensource in the polymerization processes disclosed herein include, but arenot limited to, dimethylaluminum chloride, diethylaluminum chloride,dimethylaluminum bromide, diethylaluminum bromide, dimethylaluminumfluoride, diethylaluminum fluoride, methylaluminum dichloride,ethylaluminum dichloride, methylaluminum dibromide, ethylaluminumdibromide, methylaluminum difluoride, ethylaluminum difluoride,methylaluminum sesquichloride, ethylaluminum sesquichloride,isobutylaluminum sesquichloride, methylmagnesium chloride,methylmagnesium bromide, methylmagnesium iodide, ethylmagnesiumchloride, ethylmagnesium bromide, butylmagnesium chloride,butylmagnesium bromide, phenylmagnesium chloride, phenylmagnesiumbromide, benzylmagnesium chloride, trimethyltin chloride, trimethyltinbromide, triethyltin chloride, triethyltin bromide, di-t-butyltindichloride, di-t-butyltin dibromide, dibutyltin dichloride, dibutyltindibromide, tributyltin chloride, and tributyltin bromide. In accordancewith one embodiment, the halogen source comprises an organometallichalide. For example, in accordance with certain embodiments, the halogensource comprises diethylaluminum chloride, which as mentioned above canalso serve as an alkylating agent in the lanthanide-based catalystsystem. Thus, in accordance with certain embodiments, the halogen sourcemay be provided in all or in part by the alkylating agent in thecatalyst systems disclosed herein.

The lanthanide-based catalyst composition used in this polymerizationprocesses disclosed herein may be formed by combining or mixing theforegoing catalyst ingredients. The terms “catalyst composition” and“catalyst system,” as referred to herein, encompass a simple mixture ofthe ingredients, a complex of the various ingredients that is caused byphysical or chemical forces of attraction, a chemical reaction productof the ingredients, or a combination of the foregoing. The terms“catalyst composition” and “catalyst system” can be used interchangeablyherein.

As mentioned above, a thiol compound is used as a catalyst modifier toincrease the cis-1,4-linkage content of polydienes produced using alanthanide-based catalyst system. A polydiene prepared using at leastone thiol compound in accordance with the polymerization processesdisclosed herein will have a higher cis-1,4-linkage content than apolydiene prepared under the same polymerization conditions, i.e., thesame reaction ingredients and reaction conditions, but without the thiolcompound. Thus, the polymerization processes disclosed herein are animprovement over polymerization processes that produce high-cispolydienes using lanthanide-based catalyst systems without the thiolcompound.

In accordance with the polymerization processes described herein, thethiol compound is represented by the general formula R—S—H, where R is ahydrocarbyl group or a substituted hydrocarbyl group. The practice ofthe polymerization processes disclosed herein is not limited to thiolcompounds having any particular size or type of R, i.e., hydrocarbylgroup or substituted hydrocarbyl group. For example, non-limitingexamples of types of R include alkyl, cycloalkyl, substitutedcycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, alkynyl,allyl, aryl, substituted aryl, aralkyl, and alkaryl groups. R preferablyhas 100 carbon atoms or less (e.g., 4-100 carbon atoms), more preferably30 carbon atoms or less, and even more preferably from 4 to 30 carbonatoms. Further, in one or more embodiments, the hydrocarbyl groups orsubstituted hydrocarbyl groups useful in the thiol compounds disclosedherein may contain heteroatoms such as, for example, nitrogen, oxygen,silicon, sulfur, and phosphorus atoms. In certain embodiments, thesubstituted hydrocarbyl groups may include, but are not limited to,halo-substituted or amino-substituted hydrocarbyl groups.

Examples of suitable types of thiol compounds useful in thepolymerization processes disclosed herein and represented by the generalformula R—S—H include, but are not limited to, alkanethiols, substitutedalkanethiols, cycloalkanethiols, substituted cycloalkanethiols,alkenethiols, substituted alkenethiols, cycloalkenethiols, substitutedcycloalkenethiols, arenethiols, substituted arenethiols, aralkanethiols,alkarenethiols, and the like.

Examples of suitable alkanethiols for use as the thiol compound in thepolymerization processes disclosed herein include, but are not limitedto, methanethiol; ethanethiol; propanethiols such as 1-propanethiol(n-propyl mercaptan) and 2-propanethiol; butanethiols such as1-butanethiol (n-butyl mercaptan) and 2-methylpropane-2-thiol (t-butylmercaptan); pentanethiols such as 1-pentanethiol, 2-pentanethiol,3-pentanethiol, and t-pentanethiol (t-pentyl mercaptan); hexanethiolssuch as 1-hexanethiol; heptanethiols such as 1-heptanethiol (n-heptylmercaptan) and 2-heptanethiol; octanethiols such as 1-octanethiol(n-octyl mercaptan), 2-ethylhexanethiol, and2,4,4-trimethyl-2-pentanethiol (t-octyl mercaptan); nonanethiols such as1-nonanethiol (n-nonyl mercaptan) and t-nonanethiol (t-nonyl mercaptan);decanethiols such as 1-decanethiol; undecanethiols such as1-undecanethiol; dodecanethiols such as 1-dodecanethiol andt-dodecanethiol (t-dodecyl mercaptan); tridecanethiols;tetradecanethiols such as 1-tetradecanethiol; pentadecanethiols such as1-pentadecanethiol; hexadecanethiols such as 1-hexadecanethiol;heptadecanethiols; octadecanethiols such as 1-octadecanethiol;nonadecanthiols; eicosanethiols; triacontanethiols; tetracontanethiols;pentacontanethiols; hexacontanethiols; heptacontanethiols;octacontanethiols; nonacontanethiols; hectanethiols; and the like.

Examples of suitable cycloalkanethiols for use as the thiol compound inthe polymerization processes disclosed herein include, but are notlimited to, cyclopropanethiol, cyclobutanethiol, cyclopentanethiol,cyclohexanethiol, cycloheptanethiol, cyclooctanethiol, cyclononanethiol,cyclodecanethiol, 1-adamantanethiol, and the like.

Examples of suitable substituted cycloalkanethiols for use as the thiolcompound in the polymerization processes disclosed herein include, butare not limited to, halo-substituted cycloalkanethiols such as4-fluorocyclohexanethiol, amino-substituted cycloalkanethiols such as3-dimethylaminocyclohexanethiol, and the like.

Examples of suitable alkenethiols for use as the thiol compound in thepolymerization processes disclosed herein include, but are not limitedto, propenethiols such as 2-propene-1-thiol, butenethiols such as3-butene-1-thiol, pentenethiols such as 4-pentene-1-thiol,octadecenethiols such as cis-9-octadecene-1-thiol, and the like.

Examples of suitable cycloalkenethiols for use as the thiol compound inthe polymerization processes disclosed herein include, but are notlimited to, cyclopentenethiols, cyclohexenethiols, and the like.

Examples of suitable substituted cycloalkenethiols include, but are notlimited to, alkylcycloalkenethiols such as4-trifluoromethyl-3-cyclohexene-1-thiol.

Examples of suitable arenethiols for use as the thiol compound in thepolymerization processes disclosed herein include, but are not limitedto, benzenethiol; naphthalenethiols such as 1-naphthalenethiol;terphenylthiols such as 1,1′,4′,1″-terphenyl-4-thiol; and the like.

Examples of suitable substituted arenethiols for use as the thiolcompound in the polymerization processes disclosed herein include, butare not limited to, alkyl-substituted benzenethiols such asmethylbenzenethiols, ethylbenzenethiols, propylbenzenethiols,butylbenzenethiols, and the like; polyalkyl-substituted benezenethiols,i.e., benzenethiols having 2 or more alkyl groups; halo-substitutedbenzenethiols such as 2-fluorothiophenol; amino substituted arenethiolssuch as 3-aminobenzenethiol; and the like. Non-limiting examples ofsuitable methylbenzenethiols include 2-methylbenzenethiol,3-methylbenzenethiol, and 4-methylbenzenethiol.

Examples of suitable aralkanethiols for use as the thiol compound in thepolymerization processes disclosed herein include, but are not limitedto, phenylalkanethiols such as phenylmethanethiol (phenylmethylmercaptan), phenylethanethiol (phenylethyl mercaptan),phenylpropanethiols such as 3-phenyl-1-propanethiol, phenylbutanethiols,and the like.

In accordance with one or more embodiments of the polymerizationprocesses disclosed herein, the thiol compound is selected from thegroup consisting of ethanethiol, propanethiols, butanethiols,pentanethiols, hexanethiols, heptanethiols, octanethiols, nonanethiols,decanethiols, dodecanethiols, tridecanethiols, tetradecanethiols,pentadecanethiols, hexadecanethiols, heptadecanethiols,octadecanethiols, nonadecanthiols, eicosanethiols, triacontanethiols,benzenethiol, alkyl-substituted benzenethiols, and combinations thereof.

In accordance with preferred embodiments of the polymerization processesdisclosed herein, the thiol compound used is a tertiary thiol. As usedherein, “tertiary thiol” refers to a thiol compound that has the thiolgroup located adjacent to the tertiary conformation of an alkyl group.Suitable tertiary thiols are represented by the general formula(R′)(R″)(R′″)C—S—H, where each of R′, R″, and R′″ are hydrocarbyl orsubstituted hydrocarbyl groups. In accordance with this general formula,each of R′, R″, and R′″ are bonded to the carbon atom, C, which is inturn bonded to the sulfur atom in the thiol group, S—H. Preferably, inaccordance with the thiol compounds disclosed herein, the tertiary thiolhas 100 total carbons or less, more preferably 30 carbon atoms or less,and even more preferably from 4 to 30 carbon atoms. One skilled in theart would recognize tertiary thiols include several thiol compoundsdisclosed above. Non-limiting examples of suitable tertiary thiolsinclude 2-methylpropane-2-thiol (t-butyl mercaptan), t-pentanethiol(t-pentyl mercaptan), 2,4,4-trimethyl-2-pentanethiol (t-octylmercaptan), t-nonanethiol (t-nonyl mercaptan), t-dodecanethiol(t-dodecyl mercaptan), and the like. Additional tertiary thiols that maybe useful in the practice of the polymerization processes disclosedherein may occur to those of skill in the art.

Without intending to be limited by any theory, it is believed that thesteric hindrance caused by the tertiary thiol improves thestereospecificity of the polymerization processes using thelanthanide-based catalyst system because it produces polydienes with ahigher cis content than the same process that uses non-tertiary thiols,e.g., primary or secondary thiols. For example, Examples 2-6 disclosedherein and summarized in Table 1 use a tertiary thiol (t-dodecanethiol)as the thiol compound. Examples 8-10 disclosed herein and summarized inTable 2 use 1-dodecanethiol. These two respective thiol compounds aredifferent isomers of a 12 carbon thiol compound. Examples 6 and 8 usethe same molar ratio of thiol compound to neodymium and thereforeprovide the basis for comparison between the two 12 carbon thiols, onetertiary and one non-tertiary. As shown in Example 6 of Table 1, the useof the t-dodecanethiol results in a higher cis-1,4-linkage contentcompared to its control (Example 1) than that of Example 8 shown inTable 2 compared to its control (Example 7). The difference between thecis content in the polydiene of Example 6 compared to the controlpolydiene of Example 1 is 3.58% (=98.07%-94.49%) as compared to thedifference between the cis content in the polydiene of Example 8compared to the control polydiene of Example 7 of 0.07%(=94.64%-94.57%).

The solution polymerization processes disclosed herein are preferablyconducted under anaerobic conditions under a blanket of inert gas, suchas nitrogen, argon, or helium. The polymerization temperature may varywidely, ranging from −50° C. to 150° C., with the preferred temperaturerange being 50° C. to 120° C. The polymerization pressure may also varywidely, ranging from 1 atmosphere (atm) to 30 atm, preferably 1 atm to10 atm.

The solution polymerization processes disclosed herein are conducted asa continuous, a semi-continuous, or a batch process. In thesemi-continuous process, the monomer is intermittingly charged toreplace the monomer that has already polymerized. The polymerization ofa conjugated diene monomer into a high-cis polydiene in accordance withthe processes described herein occurs when the monomer, the thiolcompound, and the lanthanide-based catalyst composition are all presentin the organic solvent-based solution. The order of addition of themonomer, thiol compound, and catalyst to the organic solvent does notmatter. However, the process is more effective, i.e., a highercis-1,4-linkage content is obtained, when the lanthanide-based catalystcomposition is added at the same time or shortly after the thiolcompound has been added to the polymerization solution. In a preferredembodiment, the lanthanide-based catalyst composition is added after thethiol compound has been added to the polymerization solution.

The polymerization processes disclosed herein can be stopped by addingany suitable terminating agent. Non-limiting examples of suitableterminating agents include protic compounds, such as alcohols,carboxylic acids, inorganic acids, water, and mixtures thereof. Thepolymerization process disclosed herein also can be stopped by afunctionalizing agent. Functionalizing agents include compounds orreagents that can react with a reactive polymer produced by thepolymerization processes disclosed herein and thereby provide thepolymer with a functional group. Other suitable terminating agents areknown to those skilled in the art. Furthermore, once the polymerizationhas been stopped, the resulting high-cis polydiene can be recovered fromthe solution using conventional methods, e.g., steam desolventization,coagulation with an alcohol, filtration, purification, drying, etc.,known to those skilled in the art.

In the polymerization processes disclosed herein, the molar ratio of thethiol compound to the lanthanide compound, i.e., part (a) of thelanthanide-based catalyst composition, ranges from 0.01:1 to 100:1. Incertain embodiments, the ratio is preferably from 0.2:1 to 12:1.

In certain embodiments, the number average molecular weight (“M_(n)”) ofthe high-cis polydienes resulting from the polymerization processesdisclosed herein ranges from 20,000 to 250,000; in other embodimentsfrom 70,000 to 130,000; and in other embodiments from 80,000 to 120,000as determined by gel permeation chromatography (“GPC”). The GPCmeasurements disclosed herein are calibrated with polystyrene standardsand Mark-Houwink constants for the high-cis polydienes produced.

In certain embodiments, the weight average molecular weight (“M_(w)”) ofthe resulting high-cis polydienes resulting from the polymerizationprocesses disclosed herein ranges from 30,000 to 600,000; from 160,000to 240,000; and in other embodiments from 170,000 to 230,000 asdetermined by GPC.

In certain embodiments, the polydispersity (M_(w)/M_(n)) of thepolydienes resulting from the polymerization processes disclosed hereinranges from 1.5 to 3.5, and in other embodiments ranges from 1.8 to 2.5.

In certain embodiments, the high-cis polydienes resulting from thepolymerization processes described herein have a Mooney viscosity(“ML₁₊₄”) ranging from 5 to 85, preferably from 25 to 50. The Mooneyviscosities disclosed herein are determined at 100° C. by a AlphaTechnologies Mooney viscometer with a large rotor, a one minute warm-uptime, and a four minute running time.

The high-cis polydienes resulting from the polymerization processesdisclosed herein are useful in rubber compositions such as those thatmay ultimately be used in tire components. The high-cis polydienes havetensile, abrasion resistance, rolling resistance, and fatigue resistanceproperties that are desirable in rubber compositions used in tirecomponents, particularly in the rubber compositions used in the tread orthe sidewall components of tires. As is known to those skilled in theart, the high-cis polydienes resulting from the polymerization processesdisclosed herein can be used alone or in combination with other rubberypolymers, including natural or synthetic elastomers to produce suchrubber compositions useful for tire components. Synthetic elastomers canbe derived from the polymerization of one or more different types ofconjugated diene monomers or the copolymerization of conjugated dienemonomers with other monomers such as vinyl-substituted aromaticmonomers.

The solution polymerization processes disclosed herein produce ahigh-cis polydiene by polymerizing at least one conjugated diene monomerin an organic solvent in the presence of at least one thiol compound anda lanthanide-based catalyst composition to produce a polydiene having acis-1,4-linkage content of 90-99%. The at least one thiol compound isrepresented by the general formula R—S—H, where R is a hydrocarbyl groupor a substituted hydrocarbyl group. The lanthanide-based catalystcomposition comprises (a) a lanthanide compound, (b) an alkylatingagent, and (c) a halogen source, where (c) may optionally be provided by(a), (b), or both (a) and (b). The molar ratio of the at least one thiolcompound to the lanthanide compound used in the polymerization processranges from 0.01:1 to 100:1.

In accordance with certain embodiments, the processes further comprisesadding the at least one thiol compound to a mixture of the at least oneconjugated diene monomer and the organic solvent prior to adding thelanthanide-based catalyst composition to the mixture.

Furthermore, in certain of the preceding embodiments, the at least onethiol compound is selected from the group consisting of ethanethiol,propanethiols, butanethiols, pentanethiols, hexanethiols, heptanethiols,octanethiols, nonanethiols, decanethiols, dodecanethiols,tridecanethiols, tetradecanethiols, pentadecanethiols, hexadecanethiols,heptadecanethiols, octadecanethiols, nonadecanthiols, eicosanethiols,triacontanethiols, benzenethiol, alkyl-substituted benzenethiols, andcombinations thereof. In certain of the preceding embodiments, the atleast one thiol compound comprises a tertiary thiol.

Moreover, in certain of the preceding embodiments, the molar ratio ofthe at least one thiol compound to the lanthanide compound ranges from0.2:1 to 12:1. In certain of the preceding embodiments, the lanthanidecompound is selected from the group consisting of lanthanidecarboxylates, lanthanide organophosphates, lanthanideorganophosphonates, lanthanide organophosphinates, lanthanidecarbamates, lanthanide dithiocarbamates, lanthanide xanthates,lanthanide β-diketonates, lanthanide alkoxides or aryloxides, lanthanidehalides, lanthanide pseudo-halides, lanthanide oxyhalides,organolanthanide compounds, and combinations thereof. The lanthanideportion of the lanthanide compound is selected from the group consistingof lanthanum, cerium, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium, didymium, and combinations thereof.

Moreover, in certain of the preceding embodiments, the alkylating agentincludes at least one organoaluminum compound, at least oneorganomagnesium compound, or combinations thereof. Further to this andall preceding embodiments, the at least one organoaluminum compound isselected from the group consisting of an aluminoxane, a compoundrepresented by the general formula AlR_(n)X_(3-n), and combinationsthereof, where R is a monovalent organic group attached to the aluminumatom via a carbon atom; X is a hydrogen atom, a halogen atom, acarboxylate group, an alkoxide group, or an aryloxide group; and n isfrom 1 to 3. Further to this and all preceding embodiments, thealkylating agent includes at least one aluminoxane and at least oneorganoaluminum compound other than aluminoxane.

In certain of the preceding embodiments, the halogen source includes anelemental halogen, a mixed halogen, a hydrogen halide, an organichalide, an inorganic halide, a metallic halide, an organometallichalide, or combinations thereof. Further to this and all precedingembodiments, the at least one conjugated diene monomer used in thepolymerization process is a monomer selected from the group consistingof 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, 2,4-hexadiene, and combinations thereof.

As previously mentioned, embodiments of the polymerization processesdisclosed herein take place in a solution containing a molar ratio from0.01:1 to 100:1 of thiol compound to lanthanide compound and theresulting polydiene has a cis-1,4-linkage content of 90-99%. In certainof these embodiments, any or all of the following (i)-(v) also apply:(i) the polymerization process takes place at 50° C. to 120° C.; (ii)the polydiene has a polydispersity value of 1.5 to 3.5; (iii) thepolydiene has between 94-99% cis-1,4-linkage content; (iv) the polydieneis polybutadiene; and (v) the polymerization takes place in the presenceof 20-90 wt % organic solvent based on the total weight of the monomer,organic solvent, and polydiene. Further in accordance with certain ofthe preceding embodiments, the polymerization takes place in thepresence of 70-90 wt % organic solvent based on the total weight of themonomer, organic solvent, and polydiene.

In certain embodiments, the solution polymerization process is animprovement to producing a high-cis polydiene by polymerizing at leastone conjugated diene monomer in an organic solvent charged with alanthanide-based catalyst composition. The improvement is directed tothe use of at least one thiol compound in the polymerization process.Restated, the improvement comprises polymerizing the at least oneconjugated diene monomer in the presence of at least one thiol compoundin the organic solvent charged with the lanthanide-based catalystcomposition to produce a polydiene having a cis-1,4-linkage content of90-99%. The improvement is shown in the resulting polydiene, where thepolydiene produced has a higher cis-1,4-linkage content compared to apolydiene produced under the same polymerization conditions but withoutthe at least one thiol compound. In accordance with the presentembodiment, the at least one thiol compound is represented by thegeneral formula R—S—H, where R is a hydrocarbyl group or a substitutedhydrocarbyl group. Also, the molar ratio of the at least one thiolcompound to the lanthanide compound used in embodiments of the improvedpolymerization process ranges from 0.01:1 to 100:1.

In certain embodiments, the improvement, i.e., the improved process,further comprises adding the at least one thiol compound to a mixture ofthe at least one conjugated diene monomer and the organic solvent priorto charging the mixture with the lanthanide-based catalyst composition.

Moreover, in certain embodiments, the at least one thiol compound isselected from the group consisting of ethanethiol, propanethiols,butanethiols, pentanethiols, hexanethiols, heptanethiols, octanethiols,nonanethiols, decanethiols, dodecanethiols, tridecanethiols,tetradecanethiols, pentadecanethiols, hexadecanethiols,heptadecanethiols, octadecanethiols, nonadecanthiols, eicosanethiols,triacontanethiols, benzenethiol, alkyl-substituted benzenethiols, andcombinations thereof. Further in certain embodiments, the at least onethiol compound comprises a tertiary thiol.

Moreover, in certain of the preceding embodiments, the lanthanide-basedcatalyst composition comprises (a) a lanthanide compound, (b) analkylating agent, and (c) a halogen source, where (c) may optionally beprovided by (a), (b), or both (a) and (b). In certain embodiments, themolar ratio of the at least one thiol compound to the lanthanidecompound ranges from 0.2:1 to 12:1.

In certain embodiments, the lanthanide compound is selected from thegroup consisting of lanthanide carboxylates, lanthanideorganophosphates, lanthanide organophosphonates, lanthanideorganophosphinates, lanthanide carbamates, lanthanide dithiocarbamates,lanthanide xanthates, lanthanide β-diketonates, lanthanide alkoxides oraryloxides, lanthanide halides, lanthanide pseudo-halides, lanthanideoxyhalides, organolanthanide compounds, and combinations thereof.Further in certain embodiments, the alkylating agent includes at leastone aluminoxane and at least one organoaluminum compound other thanaluminoxane.

Furthermore, in accordance with certain embodiments, the halogen sourceincludes an elemental halogen, a mixed halogen, a hydrogen halide, anorganic halide, an inorganic halide, a metallic halide, anorganometallic halide, or combinations thereof.

As previously mentioned, embodiments of the improved polymerizationprocesses disclosed herein take place in a solution containing a molarratio from 0.01:1 to 100:1 of thiol compound to lanthanide compound andthe resulting polydiene has a cis-1,4-linkage content of 90-99%. Incertain of these embodiments, any or all of the following (i)-(v) alsoapply: (i) the polymerization process takes place at 50° C. to 120° C.;(ii) the polydiene has a polydispersity value of 1.5 to 3.5; (iii) thepolydiene has between 94-99% cis-1,4-linkage content; (iv) the polydieneis polybutadiene; and (v) the polymerization takes place in the presenceof 20-90 wt % organic solvent based on the total weight of the monomer,organic solvent, and polydiene. Further in accordance with certainembodiments, the polymerization takes place in the presence of 70-90 wt% organic solvent based on the total weight of the monomer, organicsolvent, and polydiene.

Moreover, in accordance with certain embodiments, the at least one thiolcompound used in the improved polymerization process is at-dodecanethiol (t-dodecyl mercaptan), and the cis-1,4-linkage contentof the polydiene produced is at least 1.0 percentage point higher (e.g.,0.05-5.0 higher) compared to the cis-1,4-linkage content of a polydieneproduced under the same polymerization conditions but without the atleast one thiol compound. In other embodiments, the polydiene producthas a cis-1,4-linkage content that is at least 2.0 percentage pointshigher (e.g., 2.0-5.0) than a polydiene produced under the samepolymerization conditions but without the at least one thiol compound.In other embodiments, the polydiene product has a cis-1,4-linkagecontent that is at least 3.0 percentage points higher (e.g., 3.0-5.0higher) than a polydiene produced under the same polymerizationconditions but without the at least one thiol compound.

It should also be understand that encompassed within the presentdisclosure is a rubber composition (i.e., high-cis polydiene) producedby a process according to the processes described herein. In certainsuch embodiments, the rubber composition further comprises at least oneconjugated-diene containing polymer or copolymer, non-limiting examplesof which include styrene-butadiene copolymer, polybutadiene, naturalrubber and polyisoprene.

Furthermore, encompassed within the present disclosure is a tire havingat least one component containing the rubber (i.e., high-cis polydiene)produced by a process according to the processes described herein. Incertain such embodiments, the component is a tire tread.

As used in the description of the invention and the appended claims, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

All references incorporated herein by reference are incorporated intheir entirety unless otherwise stated.

The following examples are for purposes of illustration only and are notintended to limit the scope of the claims which are appended hereto.

EXAMPLES

The Mooney viscosities (ML₁₊₄) disclosed herein are determined at 100°C. by a Alpha Technologies Mooney viscometer with a large rotor. Thesample is preheated at 100° C. for 1 minute before the rotor starts. TheMooney Viscosity measurement is recorded as the torque after the rotorhas rotated 4 minutes at 100° C. The values disclosed in the Examplesfor M_(n), M_(w), M_(p) (the peak value for the M_(n) on the GPC curve),and polydispersity (M_(w)/M_(n)) are determined using GPC. The GPCmeasurements disclosed herein are calibrated with polystyrene standardsand Mark-Houwink constants for the high-cis polydienes. Themicrostructure content disclosed herein, including the cis-, trans-, andvinyl-contents (%) are determined by FTIR, i.e., the samples aredissolved in CS₂ and subjected to FTIR.

Preparation of the Pre-Formed Catalyst

To a 200 mL dry bottle purged with nitrogen was added 5.5 mL of 20.7%(wt/wt) butadiene solution in hexane (a 1,3-butadiene blend in hexane),11.3 mL of toluene, 5.2 mL of 4.75 M (mol/L) methylaluminoxane (“MAO”)solution in toluene, 0.46 mL of 0.54 M neodymium versatate (“NdV₃”)followed by 5.0 mL of 1.05 M diisobutylaluminum hydride (“DIBA”) inhexane. The mixture was aged for 2 minutes at room temperature. Then,0.93 mL of 1.07 M diethylaluminum chloride (“DEAC”) was added. Themixture was aged for 15 minutes before being used as the Pre-formedCatalyst in each respective Example below.

Examples 1-6: Polymerization of 1,3-butadiene using t-dodecanethiol(t-dodecyl mercaptan)

To six dry bottles purged with nitrogen was added hexane and a1,3-butadiene (“Bd”) blend in hexane (the blend contained 20.7% (wt/wt)Bd in hexane), resulting in 330 g of 15.0% (wt/wt) Bd solution inhexane. Then, to each of the bottles was added 0.00 (Example 1), 0.37(Example 2), 0.74 (Example 3), 1.11 (Example 4), 1.48 (Example 5), and1.85 (Example 6) mL of 0.0134 M t-dodecanethiol (also known as t-dodecylmercaptan), respectively, as shown in Table 1 below. The t-dodecanethiolwas in a solution of hexane. Each respective solution was charged with2.8 mL of the Pre-formed Catalyst described above. After the bottlescontaining the respective solutions were heated in a 65° C. water bathfor 50 minutes, the resulting polymer cements were quenched with 3 mL ofisopropanol containing 2,6-di-tert-butyl-4-methylphenol (“BHT”) toterminate the reaction, coagulate, and stabilize the polymers. Followingquenching, the resulting polybutadiene polymers were dried in adrum-dryer at 120° C. The polybutadiene polymer properties for each ofExamples 1-6 are summarized in Table 1 below.

TABLE 1 Example 1 2 3 4 5 6 t-dodecanethiol (mL) 0.00 0.37 0.74 1.111.48 1.85 t-dodecanethiol:Nd 0.0 0.2 0.4 0.6 0.8 1.0 (molar ratio) NdV₃(mmol/100 g Bd) 0.050 0.050 0.050 0.050 0.050 0.050 Nd:MAO:DIBA:DEAC1:100:21:4 1:100:21:4 1:100:21:4 1:100:21:4 1:100:21:4 1:100:21:4 (molarratio) Reaction Temperature (° C.) 65 65 65 65 65 65 Reaction Time (min)50 50 50 50 50 50 Conversion (%) 99.8 99.2 87.7 71.7 64.2 54.9 ML₁₊₄ @100° C. 26.10 21.00 16.70 14.50 15.90 15.10 T₈₀ (s) 1.73 1.60 1.46 1.601.71 1.85 GPC Results M_(n) 110,655 103,677 93,629 85,017 83,673 80,575M_(w) 194,561 186,441 178,864 169,667 181,837 177,220 M_(p) 159,024148,785 140,564 132,517 132,818 127,337 M_(w)/M_(n) 1.76 1.80 1.91 2.002.17 2.20 Microstructure by FTIR cis-1,4 (%) 94.49 96.08 97.37 97.7997.96 98.07 trans-1,4 (%) 4.84 3.30 2.03 1.56 1.40 1.27 vinyl (%) 0.670.62 0.61 0.65 0.64 0.66

As shown in Table 1, each of the polybutadienes of Examples 2-6 thatwere prepared using the thiol compound t-dodecanethiol have a highercis-1,4-linkage content than the polybutadiene of Example 1, producedunder the same polymerization conditions (i.e., the same reactioningredients and reaction conditions) but without the thiol compound.

Examples 7-10: Polymerization of 1,3-butadiene using 1-dodecanethiol

To four dry bottles purged with nitrogen was added hexane and a1,3-butadiene (“Bd”) blend in hexane (the blend contained 20.7% (wt/wt)Bd in hexane), resulting in 330 g of 15.0% (wt/wt) Bd solution inhexane. Then to each of the bottles was added 0.00 (Example 7), 0.18(Example 8), 0.37 (Example 9), and 1.47 (Example 10) mL of 0.134 M1-dodecanethiol, respectively, as shown in Table 2 below. The1-dodecanethiol was in a solution of hexane. Each respective solutionwas charged with 2.8 mL of the Pre-formed Catalyst described above.After the bottles containing the respective solutions were heated in a65° C. water bath for 50 minutes, the resulting polymer cements werequenched with 3 mL of isopropanol containing BHT to terminate thereaction, coagulate, and stabilize the polymers. Following quenching,the resulting polybutadiene polymers were dried in a drum-dryer at 120°C. The polybutadiene polymer properties for each of Examples 7-10 aresummarized in Table 2 below.

TABLE 2 Example 7 8 9 10 1-dodecanethiol (mL) 0.00 0.18 0.37 1.471-dodecanethiol:Nd 0.0 1.0 2.0 8.0 (molar ratio) NdV₃ (mmol/100 g Bd)0.050 0.050 0.050 0.050 Nd:MAO:DIBA:DEAC 1:100:21:4 1:100:21:41:100:21:4 1:100:21:4 (molar ratio) Reaction Temperature 65 65 65 65 (°C.) Reaction Time (min) 50 50 50 50 Conversion (%) 99.8 100.0 99.4 100.0ML₁₊₄ @100° C. 28.90 27.80 28.20 33.10 T₈₀ (s) 1.56 1.61 1.62 1.77 GPCResults M_(n) 113,961 112,423 113,923 120,867 M_(w) 208,585 203,647211,464 227,414 M_(p) 165,700 160,863 161,460 165,756 M_(w)/M_(n) 1.831.81 1.86 1.88 Microstructure by FTIR cis-1,4 (%) 94.57 94.64 94.7295.58 trans-1,4 (%) 4.78 4.69 4.59 3.77 vinyl (%) 0.65 0.67 0.69 0.65

As shown in Table 2, each of the polybutadienes of Examples 8-10 thatwere prepared using the thiol compound 1-dodecanethiol have a highercis-1,4-linkage content than the polybutadiene of Example 7, producedunder the same polymerization conditions but without the thiol compound.

Examples 11-16: Polymerization of 1,3-butadiene using4-methylbenzenethiol

To six dry bottles purged with nitrogen was added hexane and a1,3-butadiene (“Bd”) blend in hexane (the blend contained 20.7% (wt/wt)Bd in hexane), resulting in 330 g of 15.0% (wt/wt) Bd solution inhexane. Then to each of the bottles was added 0.00 (Example 11), 0.37(Example 12), 0.74 (Example 13), 1.11 (Example 14), 1.48 (Example 15),and 1.85 (Example 16) mL of 0.0134 M 4-methylbenzenethiol, respectively,as shown in Table 3 below. The 4-methylbenzenethiol was in a solution ofhexane. Each respective solution was charged with 2.8 mL of thePre-formed Catalyst described above. After the bottles containing therespective solutions were heated in a 65° C. water bath for 50 minutes,the resulting polymer cements were quenched with 3 mL of isopropanolcontaining BHT to terminate the reaction, coagulate, and stabilize thepolymers. Following quenching, the resulting polybutadiene polymers weredried in a drum-dryer at 120° C. The polybutadiene polymer propertiesfor each of Examples 11-16 are summarized in Table 3 below.

TABLE 3 Example 11 12 13 14 15 16 4-methylbenzenethiol (mL) 0.00 0.370.74 1.11 1.48 1.85 4-methylbenzenethiol:Nd 0.0 0.2 0.4 0.6 0.8 1.0(molar ratio) NdV₃ (mmol/100 g Bd) 0.050 0.050 0.050 0.050 0.050 0.050Nd:MAO:DIBA:DEAC 1:100:21:4 1:100:21:4 1:100:21:4 1:100:21:4 1:100:21:41:100:21:4 (molar ratio) Reaction Temperature (° C.) 65 65 65 65 65 65Reaction Time (min) 50 50 50 50 50 50 Conversion (%) 98.4 96.6 98.6 97.298.2 98.4 ML₁₊₄ @ 100° C. 27.30 26.60 25.00 24.10 23.70 22.50 T₈₀ (s)1.61 1.62 1.60 1.57 1.59 1.54 GPC Results M_(n) 112,373 111,968 110,053109,157 108,655 107,976 M_(w) 207,531 202,203 197,345 194,501 193,563189,719 M_(p) 153,674 152,724 150,001 147,314 146,495 144,884M_(w)/M_(n) 1.85 1.81 1.79 1.78 1.78 1.76 Microstructure by FTIR cis-1,4(%) 94.67 94.77 94.80 94.93 95.13 95.28 trans-1,4 (%) 4.69 4.57 4.494.33 4.13 3.98 vinyl (%) 0.63 0.66 0.71 0.74 0.74 0.73

As shown in Table 3, each of the polybutadienes of Examples 12-16 thatwere prepared using the thiol compound 4-methylbenzenethiol have ahigher cis-1,4-linkage content than the polybutadiene of Example 11,produced under the same polymerization conditions but without the thiolcompound.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the technology of this application belongs. While thepresent application has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the application, in its broaderaspects, is not limited to the specific details, the representativeembodiments, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

What is claimed is:
 1. A solution polymerization process for producing ahigh-cis polydiene, comprising: polymerizing at least one conjugateddiene monomer in an organic solvent in the presence of at least onethiol compound and a pre-formed lanthanide-based catalyst composition toproduce a polydiene having a cis-1,4-linkage of 90-99%, wherein the atleast one thiol compound is represented by the general formula R—S—H,where R is a hydrocarbyl group or a substituted hydrocarbyl group;wherein the pre-formed lanthanide-based catalyst composition comprises:(a) a lanthanide compound, (b) an alkylating agent, and (c) a halogensource, wherein (c) may optionally be provided by (a), (b), or both (a)and (b); and wherein the molar ratio of the at least one thiol compoundto the lanthanide compound ranges from 0.01:1 to 100:1.
 2. The processaccording to claim 1, wherein the molar ratio of the at least one thiolcompound to the lanthanide compound ranges from 0.2:1 to 12:1.
 3. Theprocess according to claim 1, wherein the at least one thiol compound isselected from the group consisting of ethanethiol, propanethiols,butanethiols, pentanethiols, hexanethiols, heptanethiols, octanethiols,nonanethiols, decanethiols, dodecanethiols, tridecanethiols,tetradecanethiols, pentadecanethiols, hexadecanethiols,heptadecanethiols, octadecanethiols, nonadecanthiols, eicosanethiols,triacontanethiols, benzenethiol, alkyl-substituted benzenethiols, andcombinations thereof.
 4. The process according to claim 1, wherein theat least one thiol compound comprises a tertiary thiol.
 5. The processof claim 1, further comprising adding the at least one thiol compound toa mixture of the at least one conjugated diene monomer and the organicsolvent prior to adding the pre-formed lanthanide-based catalystcomposition to the mixture.
 6. The process of claim 1, wherein thepre-formed lanthanide-based catalyst composition is added at the sametime as the thiol compound is added to the organic solvent.
 7. Theprocess of claim 1, wherein the lanthanide compound is selected from thegroup consisting of lanthanide carboxylates, lanthanideorganophosphates, lanthanide organophosphonates, lanthanideorganophosphinates, lanthanide carbamates, lanthanide dithiocarbamates,lanthanide xanthates, lanthanide β-diketonates, lanthanide alkoxides oraryloxides, lanthanide halides, lanthanide pseudo-halides, lanthanideoxyhalides, organolanthanide compounds, and combinations thereof, andthe lanthanide portion of the lanthanide compound is selected from thegroup consisting of lanthanum, cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium, didymium, andcombinations thereof; wherein the alkylating agent includes at least oneorganoaluminum compound, at least one organomagnesium compound, orcombinations thereof; and wherein the halogen source includes anelemental halogen, a mixed halogen, a hydrogen halide, an organichalide, an inorganic halide, a metallic halide, an organometallichalide, or combinations thereof.
 8. The process of claim 7, wherein theat least one organoaluminum compound is selected from the groupconsisting of an aluminoxane, a compound represented by the generalformula AlR_(n)X_(3-n), and combinations thereof, where: R is amonovalent organic group attached to the aluminum atom via a carbonatom, X is a hydrogen atom, a halogen atom, a carboxylate group, analkoxide group, or an aryloxide group, and n is from 1 to
 3. 9. Theprocess of claim 1, wherein the alkylating agent includes at least onealuminoxane and at least one organoaluminum compound other thanaluminoxane.
 10. The process of claim 1, wherein the at least oneconjugated diene monomer comprises a monomer selected from the groupconsisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, 2,4-hexadiene, and combinations thereof. 11.The process of claim 1, wherein the polymerization takes place at 50° C.to 120° C.
 12. The process of claim 1, wherein the polydiene has apolydispersity value of 1.5 to 3.5.
 13. The process of claim 1, whereinthe polydiene has between 94% and 99% cis-1,4-linkage content.
 14. Theprocess of claim 1, wherein the polydiene comprises polybutadiene. 15.The process of claim 1, wherein the polymerization takes place in thepresence of 20-90 weight % organic solvent based on the total weight ofthe monomer, organic solvent, and polydiene.
 16. An improved solutionpolymerization process for producing a high-cis polydiene bypolymerizing at least one conjugated diene monomer in an organic solventcharged with a pre-formed lanthanide-based catalyst composition, whereinthe improvement comprises: polymerizing the at least one conjugateddiene monomer in the presence of at least one thiol compound in theorganic solvent charged with the pre-formed lanthanide-based catalystcomposition to produce a polydiene having a cis-1,4-linkage content of90-99%, wherein the at least one thiol compound is represented by thegeneral formula R—S—H, where R is a hydrocarbyl group or a substitutedhydrocarbyl group; wherein the polydiene produced has a highercis-1,4-linkage content compared to a polydiene produced under the samepolymerization conditions but without the at least one thiol compound;and wherein the molar ratio of the at least one thiol compound to thelanthanide compound ranges from 0.01:1 to 100:1.
 17. The process ofclaim 16, wherein the improvement further comprises adding the at leastone thiol compound to a mixture of the at least one conjugated dienemonomer and the organic solvent prior to charging the mixture with thepre-formed lanthanide-based catalyst composition.
 18. The process ofclaim 16, wherein the at least one thiol compound comprises a tertiarythiol.
 19. The process of claim 16, wherein the polydiene comprisespolybutadiene.
 20. A solution polymerization process for producing ahigh-cis polybutadiene, comprising: polymerizing 1,3-butadiene in anorganic solvent in the presence of at least one thiol compound and apre-formed lanthanide-based catalyst composition to produce a polydienehaving a cis-1,4-linkage of 90-99%, wherein the at least one thiolcompound is represented by the general formula R—S—H, where R is ahydrocarbyl group or a substituted hydrocarbyl group; wherein thepre-formed lanthanide-based catalyst composition comprises: (a) alanthanide compound, (b) an alkylating agent, and (c) a halogen source,wherein (c) may optionally be provided by (a), (b), or both (a) and (b);and wherein the molar ratio of the at least one thiol compound to thelanthanide compound ranges from 0.01:1 to 100:1.